如何用Hibernate Criteria懒散地获取字段

问题描述

表的每一行 Person （具有名称，名字
$ $ p $ age > EntityManager em = emf.createEntityManager（）;
Session s =（Session）em.getDelegate（）;
Criteria criteria = s.createCriteria（Person.class）;
criteria.setFetchMode（age，FetchMode.SELECT）;


但SQL显示

  Hibernate：
选择
 person0_.name，
 person0_.firstname，
 person0_.age 
 from 
 SCOPE.PERSON person0_ 
  

如何让年龄延迟 ONLY / p>

解决方案

我认为懒惰模式只对关联有意义。如果您访问的是普通表格，则会加载所有字段。

如果您希望 age 字段不是出现在SQL中，因此不会被加载到内存中，然后使用投影：

pre $ Criteria crit = session.createCriteria（Person.class） ;
ProjectionList projList = Projections.projectionList（）;
projList.add（Projections.property（name））;
projList.add（Projections.property（firstname））;
crit.setProjection（projList）;

Each row of the table Person (having name, firstname and age) shall be read.

EntityManager em = emf.createEntityManager();
Session s = (Session) em.getDelegate();
Criteria criteria = s.createCriteria(Person.class);
criteria.setFetchMode("age", FetchMode.SELECT);

But the SQL shows

Hibernate:
    select
        person0_.name,
        person0_.firstname,
        person0_.age
    from
        SCOPE.PERSON person0_

How to let the age be lazy ONLY for the Criteria??

解决方案

I think that lazy mode only makes sense with associations. If you are accessing a plain table it will load all the fields.

If you want the age field not to appear in the SQL and so not being loaded into memory then use projections:

Criteria crit = session.createCriteria(Person.class);
ProjectionList projList = Projections.projectionList();
projList.add(Projections.property("name"));
projList.add(Projections.property("firstname"));
crit.setProjection(projList);

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